Electrochemical Treatment of the Antibiotic Sulfachloropyridazine: Kinetics, Reaction Pathways, and Toxicity Evolution

Abstract

The electro-Fenton treatment of sulfachloropyridazine (SCP), a model for sulfonamide antibiotics that are widespread in waters, was performed using cells with a carbon-felt cathode and Pt or boron-doped diamond (BDD) anode, aiming to present an integral assessment of the kinetics, electrodegradation byproducts, and toxicity evolution. H₂O₂ electrogeneration in the presence of Fe²⁺ yielded ^•OH in the solution bulk, which acted concomitantly with ^•OH adsorbed at the anode (BDD­(^•OH)) to promote the oxidative degradation of SCP (<i>k</i>_abs,SCP = (1.58 ± 0.02) × 10⁹ M^–1 s^–1) and its byproducts. A detailed scheme for the complete mineralization was elucidated. On the basis of the action of ^•OH onto four different SCP sites, the pathways leading to total decontamination includes fifteen cyclic byproducts identified by HPLC and GC-MS, five aliphatic carboxylic acids, and a mixture of Cl^–, SO₄^2–, NH₄⁺, and NO₃^– that accounted for 90–100% of initial Cl, S, and N. The time course of byproducts was satisfactorily correlated with the toxicity profiles determined from inhibition of <i>Vibrio fischeri</i> luminescence. 3-Amino-6-chloropyridazine and <i>p</i>-benzoquinone were responsible for the increased toxicity during the first stages. Independent electrolyses revealed that their toxicity trends were close to those of SCP. The formation of the carboxylic acids involved a sharp toxicity decrease, thus ensuring overall detoxification